SIMBAD references

Four ROSAT X-ray observations of the secondary optical minimum of the eclipsing binary system α CrB taken in 1992, 1993 and 1997 are presented. Because of the totality of the X-ray eclipse, the times of mid eclipse can be accurately determined from the ROSAT data. The period between secondary minima P_s is found to be significantly different from the optically well determined period between primary minima P_p, thus indicating apsidal motion. The observed value P_s -P_p=4.8±2.1seconds is, first, shown to be almost exclusively due to the primary component, and second, consistent with our current knowledge of α CrB A. The relativistic contribution to the observed value is 0.95seconds or 17% of the total effect.